1. Field of the Invention
The present invention relates to an electric motor having a one-way clutch and a worm gear mechanism, which is used in a power drive system such as a vehicle power window system.
2. Description of the Related Art
A motor used in a power window system has a speed reduction worm mechanism. The worm mechanism has a worm shaft which is coaxially linked to the armature shaft of the motor. When the motor rotates, the rotation speed of the motor is transmitted to the worm shaft and reduced by the worm mechanism. Thus, torque is increased and transmitted to a window regulator to open or close a window.
If a window is forced to open from outside while the motor is not operated, an outside torque is applied to rotate the motor via the window regulator. If the motor is rotated by the outside torque, the window can be opened. As a result a door can be opened without a key.
It has been proposed that a one-way clutch is inserted between the worm shaft and the armature shaft. Such a one-way clutch allows the motor to rotate the worm gear mechanism and prohibits the worm gear mechanism to rotate the motor.
However, it is difficult to insert such an ordinary one-way clutch if the armature shaft and the worm shaft is out of alignment. In addition, such a one-way clutch makes the motor size larger.